This invention relates to the art of rotary printing and deals more specifically with how to mount a printing plate to a plate cylinder in a rotary printing press. Still more specifically, the invention concerns both the printing plate having two interdigitating series of spaced mounting lugs on its pair of meeting edges for use in mounting the plate to the plate cylinder, and the plate cylinder configured specifically for that printing plate in order to permit the same to be readily and undetachably mounted thereto.
Japanese Examined Patent Publication No. 5-66264 and Japanese Unexamined Patent Publication No. 8-58064 are hereby cited as teaching how to mount printing plates to plate cylinders. The former suggests a printing plate in the form of a rectangular sheet of a so-called xe2x80x9cshape memorizingxe2x80x9d alloy of any known or suitable composition. The printing plate is formed to include a rim bent inwardly along one of its pair of meeting edges. The bent rim is intended for engagement in a groove formed in the surface of the plate cylinder and extending parallel to the cylinder axis.
The printing plate xe2x80x9cmemorizesxe2x80x9d the tubular shape of the required diameter it should take when wrapped around the plate cylinder. Therefore, supplied in flat form, the plate is to be heated, usually by application of heated air, while being mounted to the cylinder, until it rolls up and closely embraces the cylinder. The plate is said to stay firmly in place on the cylinder as the bent rim on only one of its meeting edges is engaged in the groove in the cylinder. The width of this groove may therefore be only somewhat more than the thickness of the printing plate.
Offsetting the advantages gained by this prior art printing plate are the drawbacks that arise from the same cause as do the advantages, the use of shape memorizing alloy material, which is more expensive than usual printing plate materials. The manufacturing cost of the printing plate has become even higher as the plate must be pretreated to xe2x80x9cmemorizexe2x80x9d the tubular shape. Furthermore, in use of the printing plate, the printing press must be equipped with an attachment for application of heated airstream to the plate for deforming the same into the required shape each time such a plate is mounted to the plate cylinder. The attachment itself is costly and has added to the space requirement of the press as well as to its running costs.
All these disadvantages, and advantages too, of the first recited prior art are absent from the second mentioned document, Japanese Unexamined Patent Publication No. 8-58064. This second conventional printing plate takes the form of a rectangular piece of flexible sheet material, having a row of alternately bent and unbent lugs projecting from one of its meeting edges. Along the other of the meeting edges there are formed a series of bent lugs alternating with recesses which are shaped and sized to receive the unbent lugs on the first mentioned of the meeting edges. When the plate is wrapped around the plate cylinder, the bent lugs on both meeting edges come into face-to-face abutment against each other as they are received in a groove in the surface of the cylinder. Further, on the surface of the cylinder, the unbent lugs on the first meeting edge fit in the recesses in the second.
Being required to receive the two butting series of bent lugs on both meeting edges of the second prior art printing plate, the groove in the plate cylinder has had to be more than twice as wide as the thickness of the plate. The inconveniently wide groove has necessitated the provision of the unbent lugs on the first meeting edge, for partly closing the groove, and the creation of the recesses in the second meeting edge for receiving the unbent lugs.
So complex in shape and exacting in dimensions and locations, the meeting edge configurations of the second prior art printing plate were very difficult of production. They were, indeed, incapable of creation by the bending machines that had been more conventionally used for jointly bending the meeting edges of printing plates. A dedicated bending machine of complex, expensive construction had to be newly installed for production of printing plates according to the teachings of the second prior art.
It will of course be understood that the two noted conventional devices cannot possibly be combined to provide a printing plate that is free from the drawbacks of both devices. The first described prior art printing plate attains its simplicity of construction, and makes it possible to narrow the groove in the plate cylinder to a minimum, only at the cost of the expensive material in use. The complex meeting edge configurations of the second described prior art printing plate, and the resulting wider groove in the plate cylinder, have been the direct results, conventionally, of the cheaper material of which the plate is made. The two devices are contradictory and incompatible.
In view of the foregoing state of the art, the present invention has it as an object to provide a printing plate that can be made from inexpensive, ordinary printing plate materials and that is easy to fabricate with conventional, readily available machinery.
Another object of the invention is to provide a printing plate that is mountable to an associated plate cylinder having a groove comparable in width to that conventionally used with the shape memorizing printing plate.
Yet another object of the invention is to expedite the process of mounting a printing plate to a plate cylinder without use of any additional equipment to that end.
A further object of the invention is to provide a plate cylinder designed specifically for use with the printing plate, in order to permit the same to be readily and firmly mounted thereto.
Briefly summarized, the present invention provides a printing plate for use with a plate cylinder having formed therein a groove extending parallel to the cylinder axis. The printing plate is generally in the form of a piece of flexible sheet material integrally comprising an image-bearing major part having a pair of meeting edges which are to meet each other when the printing plate is wrapped around the plate cylinder, and two series of lugs formed on the meeting edges of the major part and bent with respect to the major part for engagement in the groove in the plate cylinder. The two series of lugs on the major part are capable of interfitting interengagement with each other in the groove in the plate cylinder.
Preferably, the groove in the plate cylinder has its depth direction set an angle to a plane tangent to the cylinder at the groove so that opposite sides of the groove are at acute and obtuse angles, respectively, to that tangential plane. In conformity with this angled groove, the two series of lugs of the printing plate are bent with respect to the major part at approximately the same acute and obtuse angles, respectively, as the opposite sides of the groove are to the tangential plane.
For mounting the printing plate to the plate cylinder, the acute-angled series of lugs of the plate are first inserted in the groove in the cylinder so as to hook these lugs onto the acute-angled trailing side of the groove. Then the plate is wrapped around the cylinder by rotating the same in a prescribed direction. Then the obtuse-angled series of lugs are inserted in the cylinder groove into an interdigitating relationship with the acute-angled series of lugs.
Being constructed and mounted to the plate cylinder as above, the printing plate according to this invention can be made from conventional printing plate materials instead of from shape memorizing, magnetic, or like expensive materials. The two staggered, bent rows of lugs of the printing plate are easy to fabricate with conventional machinery, and the completed printing plate is readily mountable to the plate cylinder, unaided by any additional equipment, without in any way adding to the toil of the operator.
It is to be noted that the two series of lugs on the mounting plate interdigitate or interfit in the cylinder groove, instead of butt against each other as in one of the cited prior art devices. Consequently, the cylinder groove can have a width less than twice the thickness of the printing plate, requiring no special means for closure of its entrance end against ink intrusion. And, the narrow cylinder groove reduces a mechanical shock between the blanket cylinder and the plate cylinder when the plate cylinder is rotating, thereby a high speed printing and a high quality print are performed.